One-way clutch

ABSTRACT

A one-way clutch includes: an inner race; an outer race; a plurality of engaging members disposed between the inner and the outer races; a pair of retainers for retaining the engaging members; springs for urging the engaging members in one direction; and a pair of end bearings which are respectively disposed on both sides between the inner race and the outer race, each of the end bearings being formed into a U-shaped cross section by a first hollow cylindrical portion fitted to an outer peripheral surface of the inner race, a second hollow cylindrical portion fitted to an inner peripheral surface of the outer race, and an annular portion connecting the first and the second hollow cylindrical portions. The one-way clutch is characterized in that recessed portions ( 11 ) are formed at least in the inner peripheral surface ( 8   a ) of the first hollow cylindrical portion ( 8 ) of each of the end bearings ( 7 ).

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a one-way clutch for use in atransmission of an automobile.

[0002] As a one-way clutch for use in a transmission of an automobile orthe like, one is conventionally known such as in Japanese ExaminedUtility Model Publication No. Hei. 7-55391. FIG. 8 shows a relatedone-way clutch and it includes an outer race 50, an inner race 51, aplurality of engaging members (sprags) 52 disposed between the inner andouter races, an inner retainer 53, an outer retainer 54, springs 55, apair of end bearings 56, and the like.

[0003] The aforementioned sprags 52 are retained by the inner retainer53, and the outer retainer 54 in a space formed by the end bearings 56fitted to opposite sides between the inner race 51 and the outer race50, and are disposed in such a manner as to be urged in one direction bythe springs 55 disposed between the inner and outer retainers 53 and 54.Each end bearing 56 is formed into a U-shaped cross section and isconstituted by a first hollow cylindrical portion 57 fitted to an outerperipheral surface 51 a of the inner race 51, a second hollowcylindrical portion 58 fitted to an inner peripheral surface 50 a of theouter race 50, and an annular portion 59 which radially connects thefirst hollow cylindrical portion 57 to the second hollow cylindricalportion 58. The annular portion 59 of each end bearing 56 having theU-shaped cross section is located on each outer side of the one-wayclutch. Each annular portion 59 has substantially the same thicknessfrom its inner periphery to its outer periphery and is formed in such amanner as to extend radially so as to be substantially perpendicular tothe axis of the inner race 51. In each of the end bearings 56, an innerperipheral surface 57 a of the first hollow cylindrical portion 57opposing the outer peripheral surface 51 a of the inner race 51, as wellas an outer peripheral surface 58 a of the second hollow cylindricalportion 58 opposing the inner peripheral surface 50 a of the outer race50, are formed as smooth surfaces.

[0004] In the above-described conventional one-way clutch, the endbearings 56 are disposed between the inner and outer races 51 and 50 andhave a function as slide bearings. Namely, the inner peripheral surface57 a of the first hollow cylindrical portion 57 slides on the outerperipheral surface 51 a of the inner race 51, and the outer peripheralsurface 58 a of the second hollow cylindrical portion 58 slides on theinner peripheral surface 50 a of the outer race 50. The clearancebetween the inner race 51 and the first hollow cylindrical portion 57 ofthe end bearing 56 and the clearance between the outer race 50 and thesecond hollow cylindrical portion 58 of the end bearing 56 are madeextremely small in view of securing the space for the sprags 52 of theone-way clutch. For this reason, there have been problems in that thefriction, i.e., the drag torque, between the inner race 51 and the firsthollow cylindrical portion 57 of the end bearing 56 and between theouter race 50 and the second hollow cylindrical portion 58 of the endbearing 56 cannot be made small, and that seizure is likely to occur.This friction constitutes a problem particularly between the inner race51 and the first hollow cylindrical portion 57. The reason is,thatconsideration is generally given to eliminate as much as possible theclearance between the outer race 50 and the second hollow cylindricalportion 58, which is located on the side where the peripheral speed islarge, so as to prevent the occurrence of sliding between the twomembers 50 and 58, whereas a clearance is provided between the innerrace 51 and the first hollow cylindrical portion 57, where theperipheral speed is small, so as to positively allow sliding to occurbetween the two members 51 and 57.

[0005] In addition, to overcome the above-described problems, anarrangement has been proposed in which, as shown in FIG. 9, axialgrooves 60 are formed at a plurality of circumferential positions in theinner peripheral surface 57 a of the first hollow cylindrical portion 57of the end bearing 56 by lathe turning machining, so as to lower thecontact area. However, since the processing of the axial grooves 60 iseffected by machining, there are problems in that the cost becomes high,and that mass productivity is poor.

SUMMARY OF THE INVENTION

[0006] In view of the above-described problems, the object of theinvention is to provide a one-way clutch which excels in massproductivity and in which friction is small.

[0007] The object of the invention is to provide a one-way clutch inwhich an axial groove for enlarging the amount of lubricating oilretained and enhancing the reduction of friction between the firsthollow cylindrical portion and the inner race is formed in the innerperipheral surface of the first hollow cylindrical portion of the endbearing.

[0008] In order to solve the aforesaid object, the invention ischaracterized by having the following arrangement.

[0009] (1) A one-way clutch comprising:

[0010] an inner race;

[0011] an outer race;

[0012] a plurality of engaging members disposed between the inner andouter races;

[0013] retainers for retaining the engaging members;

[0014] springs for urging the engaging members in one direction; and

[0015] a pair of end bearings which are respectively disposed onopposite sides between the inner race and the outer race, each of theend bearings having a U-shaped cross section and including,

[0016] a first hollow cylindrical portion fitted to an outer peripheralsurface of the inner race,

[0017] a second hollow cylindrical portion fitted to an inner peripheralsurface of said outer race,

[0018] an annular portion connecting the first hollow cylindricalportion to second hollow cylindrical portion, and

[0019] a plurality of recessed portions formed at least in the innerperipheral surface of the first hollow cylindrical portion of each ofthe end bearings.

[0020] (2) The one-way clutch according to (1), wherein the recessedportions are a plurality of dimple-like dents.

[0021] (3) The one-way clutch according to (1), wherein the recessedportions are axial grooves formed by press forming.

[0022] (4) The one-way clutch according to (1), wherein the recessedportions are axial grooves formed by press forming and a circumferentialgroove formed by press forming so as to intersect the axial grooves.

[0023] (5) A one-way clutch comprising:

[0024] an inner race;

[0025] an outer race;

[0026] a plurality of engaging members disposed between the inner andouter races;

[0027] retainers for retaining the engaging members;

[0028] springs for urging the engaging members in one direction; and

[0029] a pair of end bearings which are respectively disposed onopposite sides between the inner race and the outer race, each of theend bearings having a U-shaped cross section and including,

[0030] a first hollow cylindrical portion fitted to an outer peripheralsurface of the inner race,

[0031] a second hollow cylindrical portion fitted to an inner peripheralsurface of said outer race,

[0032] an annular portion connecting the first hollow cylindricalportion to second hollow cylindrical portion, and

[0033] a plurality of projections formed at least on the innerperipheral surface of the first hollow cylindrical portion of each ofsaid end bearings.

[0034] (6) A one-way clutch including:

[0035] an inner race;

[0036] an outer race;

[0037] a plurality of engaging members disposed between the inner andouter races;

[0038] retainers for retaining the engaging members;

[0039] springs for, urging the engaging members in one direction; and

[0040] a pair of end bearings which are respectively disposed onopposite sides between the inner race and the outer race, each of theend bearings having a U-shaped cross section and including,

[0041] a first hollow cylindrical portion fitted to an outer peripheralsurface of the inner race,

[0042] a second hollow cylindrical portion fitted to an inner peripheralsurface of said outer race,

[0043] an annular portion connecting the first hollow cylindricalportion to second hollow cylindrical portion, and

[0044] axial grooves which extend through to opposite ends of the firsthollow cylindrical portion and are formed at a plurality ofcircumferential positions at least in an inner peripheral of the firsthollow cylindrical portion of each of the end bearings, each of theaxial grooves having a circular-arc-shaped cross section in which itsradial depth becomes larger toward a central portion of the axialgroove.

[0045] (7) The one-way clutch according to (6), wherein acircumferential groove having a predetermined axial width and a bottomsurface which includes portions of the axial grooves where the radialdepth becomes maximum is formed in the inner peripheral surface of thefirst hollow cylindrical portion of each of the end bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a cross-sectional view of a one-way clutch in accordancewith an embodiment of the invention;

[0047]FIG. 2 is a cross-sectional view of an end bearing shown in FIG.1;

[0048]FIG. 3 is a cross-sectional view of the end bearing in accordancewith a second embodiment of the invention;

[0049]FIG. 4 is a cross-sectional view of the end bearing in accordancewith still a third embodiment of the invention;

[0050]FIG. 5 is a cross-sectional view of a one-way clutch in accordancewith an fourth embodiment of the invention;

[0051]FIG. 6 is an enlarged cross-sectional view of an end bearing shownin FIG. 5;

[0052]FIG. 7 is an enlarged cross-sectional view of the end bearing inaccordance with a fifth embodiment of the invention;

[0053]FIG. 8 is a cross-sectional view of a conventional one-way clutch;and

[0054]FIG. 9 is a cross-sectional view of another end bearing of aconventional one-way clutch.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0055] First Embodiment

[0056] Referring to FIGS. 1 and 2, a description will be given of afirst embodiment of the invention. A one-way clutch in accordance withthe embodiment of the invention includes an outer race 1, an inner race2, a plurality of engaging members (sprags) 3 disposed between the innerand outer races, an inner retainer 4, an outer retainer 5, springs 6, apair of end bearings 7, and the like.

[0057] The aforementioned sprags 3 are retained by the inner retainer 4and the outer retainer 5 in a space formed by the inner race 2, theouter race 1, and the end bearings 7 fitted to both sides between theinner race 2 and the outer race 1, and are disposed in such a manner asto be urged in one direction by the springs 6 disposed between the innerand outer retainers 4 and 5. Each end bearing 7 is formed into aU-shaped cross section and comprises a first hollow cylindrical portion8 fitted to an outer peripheral surface 2 a of the inner race 2, asecond hollow cylindrical portion 9 fitted to an inner peripheralsurface 1 a of the outer race 1, and an annular portion 10 whichradially connects the first hollow cylindrical portion 8 to the secondhollow cylindrical portion 9. The annular portion 10 of each end bearing7 having the U-shaped cross section is located on each outer side of theone-way clutch. Each annular portion 10 has substantially the samethickness from its inner periphery to its outer periphery and is formedin such a manner as to extend radially so as to be substantiallyperpendicular to the axis of the inner race 2.

[0058] Recessed portions for reducing friction are formed in outersurfaces of each of the above-described end bearings 7, i.e., an innerperipheral surface 8 a of the first hollow cylindrical portion 8opposing the outer peripheral surface 2 a of the inner race 2, an outerperipheral surface 9 a of the second hollow cylindrical portion 9opposing the inner peripheral surface 1 a of the outer race 1, and anoutside surface 10 a of the annular portion 10. As an example of theserecessed portions, in FIGS. 1 and 2, a multiplicity of dimple-like dents11 are formed, respectively. The dents 11 may be formed in the innerperipheral surface 8 a of the first hollow cylindrical portion 8 and theouter peripheral surface 9 a of the second hollow cylindrical portion 9which are the sliding surfaces, but the dents 11 are indispensableparticularly in the inner peripheral surface 8 a of the first hollowcylindrical portion 8. As can be fully understood from the descriptionof the conventional structure, the reason for this is that considerationis generally given to eliminate as much as possible the clearancebetween the outer race 1 and the second hollow cylindrical portion 9,which is located on the side where the peripheral speed is large, so asto prevent the occurrence of sliding between the two members 1 and 9,whereas a clearance is provided between the inner race 2 and the firsthollow cylindrical portion 8, where the peripheral speed is small, so asto positively allow sliding to occur between the two members 1 and 8.

[0059] The aforementioned end bearing 7 is formed as follows. Adoughnut-shaped disk having a predetermined length in the radiallydeforming direction is stamped out from a metallic thin plate by pressworking. At this time, the dimple-like dents 11 having a predetermineddepth are simultaneously formed in overall surface at one side by diepressing. Subsequently, the inner and outside radial portions aresubjected to drawing by press working to form the first hollowcylindrical portion 8 and the second hollow cylindrical portion 9 suchthat the dimple-like dents 11 appear on the outside surface side. As aresult, the end bearing 7 shown in FIG. 2 is formed.

[0060] Since the above-described processing of the dimple-like dents iseffected for the entire surface, die working is facilitated since it isnot so important to take into consideration the positions of the dents11; however, unnecessary dents 11 are formed in the outside surface 10 aof the annular portion 10 as well. In a case where there is a need toavoid this, it suffices if, when the doughnut-shaped disk is stampedout, the dimple-like dents 11 are formed only in a radial area forforming the first hollow cylindrical portion 8 or in radial areas forforming the first hollow cylindrical portion 8 and the second hollowcylindrical portion 9. If this arrangement is adopted, the dents 11 areformed only in the inner peripheral surface 8 a of the first hollowcylindrical portion 8 or in both the inner peripheral surface 8 a of thefirst hollow cylindrical portion 8 and the outer peripheral surface 9 aof the second hollow cylindrical portion 9, which constitute the slidingsurfaces. As described before, these dents 11 must be formed at least inthe inner peripheral surface 8 a of the first hollow cylindrical portion8, as described before.

[0061] Second Embodiment

[0062]FIG. 3 shows a second embodiment of the present invention in whichaxial grooves 12 are formed at a plurality of circumferential positionsin the inner peripheral surface 8 a of the first hollow cylindricalportion 8 by press working, and one circumferential groove 14 whichintersects these axial grooves 12 is simultaneously formed by pressworking. These axial grooves continue from an end of the first hollowcylindrical portion 8 to the outside surface 10 a of the annular portion10 to allow lubricating oil to circulate. In addition, although, in FIG.3, these axial grooves 12 are formed only in the inner peripheralsurface 8 a of the first hollow cylindrical portion 8, the axial grooves12 may be formed also in the outer peripheral surface 9 a of the secondhollow cylindrical portion 9, as necessary. Furthermore, the axialgrooves 12 may be formed in the entire outer surfaces of the end bearing7, i.e., the inner peripheral surface 8 a of the first hollowcylindrical portion 8, the outer peripheral surface 9 a of the secondhollow cylindrical portion 9, and the outside surface 10 a of theannular portion 10. In addition, a plurality of circumferential grooves14 may be provided in the axial direction, or either one of thecircumferential groove(s) 14 and the axial grooves 12 may be omitted, asnecessary. In addition, the press working of the axial grooves 12 andthe circumferential groove(s) 14 is effected in the same way asdescribed with reference to FIG. 2.

[0063] Third Embodiment

[0064]FIG. 4 shows a third embodiment in which a multiplicity ofprojections 13 are formed on the outer surfaces of the end bearing 7,i.e., the inner peripheral surface 8 a of the first hollow cylindricalportion 8, the outer peripheral surface 9 a of the second hollowcylindrical portion 9, and the outside surface 10 a of the annularportion 10. It suffices if the projections 13 are formed on the innerperipheral surface 8 a of the first hollow cylindrical portion 8 and theouter peripheral surface 9 a of the second hollow cylindrical portion 9,which are the sliding surfaces, but the projections 13 are indispensableparticularly on the inner peripheral surface 8 a of the first hollowcylindrical portion 8. The reason for this has already been describedwith reference to FIG. 2. In addition, these projections 13 are alsoworked by press forming, and the working process is the same as in FIG.2.

[0065] Fourth Embodiment

[0066] Referring to FIGS. 5 and 6, a description will be given of afourth embodiment of the invention. A one-way clutch in accordance withthe embodiment of the invention comprises an outer race 101, an innerrace 102, a plurality of engaging members (sprags) 103 disposed betweenthe inner and outer races, an inner retainer 104, an outer retainer 105,springs 106, a pair of end bearings 107, and the like.

[0067] The aforementioned sprags 103 are retained by the inner retainer104 and the outer retainer 105 in a space formed by the inner race 102,the outer race 101 and the end bearings 107 fitted to opposite sidesbetween the inner race 102 and the outer race 101, and are disposed insuch a manner as to be urged in one direction by the springs 106disposed between the inner and outer retainers 104 and 105. Each endbearing 107 is formed into a U-shaped cross section and includes a firsthollow cylindrical portion 108 fitted to an outer peripheral surface 102a of the inner race 102, a second hollow cylindrical portion 109 fittedto an inner peripheral surface 101 a of the outer race 101 and anannular portion 110 which radially connects the first hollow cylindricalportion 108 to the second hollow cylindrical portion 109. The annularportion 110 of each end bearing 107 with the U-shaped cross section islocated on each outer side of the one-way clutch. Each annular portion110 has substantially the same thickness from its inner periphery to itsouter periphery and is formed in such a manner as to extend radially soas to be substantially perpendicular to the axis of the inner race 102.

[0068] To reduce friction between the first hollow cylindrical portion108 and the inner race 102, a plurality of axial grooves 111, whichserve as lubricating oil reservoirs, are formed on the circumference ofan outer surface of each end bearing 107, i.e., an inner peripheralsurface 8 a of the first hollow cylindrical portion 108 opposing theouter peripheral surface 102 a of the inner race 102, in such a manneras to extend through to opposite ends of the first hollow cylindricalportion 108. Each of these axial grooves 111 has a circular-arc-shapedcross section in which the radial depth becomes larger toward itscentral portion. Namely, the axial groove 11 is formed in such a waythat the circular-arc-shaped surface becomes gradually deeper in theradial direction from its both ends 111 a and 111 b toward its axiallycentral portion 111 c. It should be noted that these axial grooves areformed by cutting or press forming, and their maximum depth is set toapproximately 0.2 to 0.5 mm or thereabouts.

[0069] In the fourth embodiment shown in FIGS. 5 and 6, lubricating oilreservoirs are formed in the entire axial surface of the first hollowcylindrical portion 108 of the end bearing 107 by the above-describedaxial grooves 111, with the result that the sliding portion between theentire surface of the inner peripheral surface 108 a of the first hollowcylindrical portion 108 of the end bearing 107 and the entire surface ofthe outer peripheral surface 102 a of the inner race 102 is constantlylubricated sufficiently, thereby improving the anti-seizurecharacteristic. In addition, the contact area between the first hollowcylindrical portion 108 and the inner race 102 can be substantiallyreduced by the plurality of axial grooves 111, which, together with theabove-described sufficient lubrication, makes it possible to enhance thereduction of friction between the first hollow cylindrical portion 108and the inner race 102. Further, since the axial grooves havecircular-arc-shaped cross sections, the amount of lubricating oilretained is large, and since the lubricating oil is collected bycentrifugal force on the circular-arc-shaped surfaces extending fromboth ends 111 a and 111 b toward the central portion 111 c of the axialgrooves 11, a shortage of the supply of lubricating oil does not occur.

[0070] Fifth Embodiment

[0071]FIG. 7 shows a fifth embodiment of the invention. In a one-wayclutch in accordance with the embodiment of the invention, a pluralityof axial grooves 111 having utterly identical structure of the axialgrooves in the fourth embodiment shown in FIGS. 5 and 6, and acircumferential groove 112 having a predetermined axial width whichincludes portions of the central portion 111 c of the axial grooves 11where the radial depth becomes maximum are formed at the innerperipheral surface 108 a of the first hollow cylindrical portion 108 offeach end bearing 107. In the fifth embodiment shown in FIG. 7, ascompared with the fourth embodiment shown in FIGS. 5 and 6, the functionof lubricating oil reservoirs improves by the portion in which thecircumferential groove 112 is added, and the effect of reducing frictionbecomes greater.

[0072] It should be noted that although, in the above-described twoembodiments, the axial grooves 111, or the axial grooves 111 and thecircumferential groove 112, are formed in the inner peripheral surface108 a of the first hollow cylindrical portion 108, the grooves 111 and112 may be formed also in the outer peripheral surface 109 a of thesecond hollow cylindrical portion 109.

[0073] Experiment

[0074] A table 1 shows an experimental result of friction measurement ofthe one-way clutch having the recessed portions at the end bearing as inthe second Embodiment of the present invention in comparison with thatin the conventional art in which the end bearing having no recessedportion. Experiment condition:

[0075] Inner race: rotating, Outer race: fixed

[0076] Temperature: Normal temperature

[0077] Oil feed rate: 100 cc/min TABLE 1 Experimental result of Frictionmeasurement Inner race rotational frequency 1500 rpm 3000 rpm Endbearing having recessed 0.50 N*m 0.45 N*m portion End bearing having norecessed 0.83 N*m 0.97 N*m portion

[0078] With the one-way clutch according to the invention, sincerecessed portions are formed in the inner peripheral surface of thefirst hollow cylindrical portion of each end bearing which is the sidewhere sliding particularly occurs, it is possible to reduce a contactarea for the inner race, thereby making it possible to reduce friction,i.e., drag torque.

[0079] In addition, a lubricating oil film is likely to be formed byvirtue of a multiplicity of recesses and projections, thereby making itpossible to improve the anti-seizure characteristic.

[0080] Furthermore, since the axial grooves are formed not by machiningbut by press forming, the one-way clutch excels in mass productivity andmakes it possible to reduce cost.

[0081] Further according to the invention, lubricating oil reservoirsare formed in the entire axial surface of the first hollow cylindricalportion of the end bearing by the axial grooves, so that the slidingportion between the entire surface of the inner peripheral surface ofthe first hollow cylindrical portion and the entire surface of the outerperipheral surface of the inner race is constantly lubricatedsufficiently, thereby improving the anti-seizure characteristic. Inaddition, the contact area between the first hollow cylindrical portionand the inner race can be substantially reduced by the plurality ofaxial grooves, which, together with the above-described sufficientlubrication, makes it possible to enhance the reduction of frictionbetween the first hollow cylindrical portion and the inner race.Further, since the axial grooves have circular-arc-shaped crosssections, the amount of lubricating oil retained is large, and since thelubricating oil is collected by centrifugal force on thesecircular-arc-shaped surfaces, a shortage of the supply of lubricatingoil does not occur.

[0082] In addition, the arrangement provided is such that formed in theinner peripheral surface of the first hollow cylindrical portion of eachof the end bearings are the axial grooves with circular-arc-shaped crosssections and a circumferential groove a circumferential groove with apredetermined axial width, which includes portions of the centralportions of the axial grooves where the radial depth becomes maximum, isadditionally formed therein. The lubricating oil reservoirs are thusmade larger, and the effect of reducing friction becomes larger.

What is claimed is
 1. A one-way clutch comprising: an inner race; anouter race; a plurality of engaging members disposed between the innerand outer races; retainers for retaining the engaging members; springsfor urging the engaging members in one direction; and a pair of endbearings which are respectively disposed on opposite sides between theinner race and the outer race, each of the end bearings having aU-shaped cross section and including, a first hollow cylindrical portionfitted to an outer peripheral surface of the inner race, a second hollowcylindrical portion fitted to an inner peripheral surface of said outerrace, an annular portion connecting the first hollow cylindrical portionto second hollow cylindrical portion, and a plurality of recessedportions formed at least in the inner peripheral surface of the firsthollow cylindrical portion of each of the end bearings.
 2. The one-wayclutch according to claim 1, wherein the recessed portions are aplurality of dimple-like dents.
 3. The one-way clutch according to claim1, wherein the recessed portions are axial grooves formed by pressforming.
 4. The one-way clutch according to claim 1, wherein therecessed portions are axial grooves formed by press forming and acircumferential groove formed by press forming so as to intersect theaxial grooves.
 5. A one-way clutch comprising: an inner race; an outerrace; a plurality of engaging members disposed between the inner andouter races; retainers for retaining the engaging members; springsfor,urging the engaging members in one direction; and a pair of endbearings which are respectively disposed on opposite sides between theinner race and the outer race, each of the end bearings having aU-shaped cross section and including, a first hollow cylindrical portionfitted to an-outer peripheral surface of the inner race, a second hollowcylindrical portion fitted to an inner peripheral surface of said outerrace, an annular portion connecting the first hollow cylindrical portionto second hollow cylindrical portion, and a plurality of projectionsformed at least on the inner peripheral surface of the first hollowcylindrical portion of each of said end bearings.
 6. A one-way clutchincluding: an inner race; an outer race; a plurality of engaging membersdisposed between the inner and outer races; retainers for retaining theengaging members; springs for urging the engaging members in onedirection; and a pair of end bearings which are respectively disposed onopposite sides between the inner race and the outer race, each of theend bearings having a U-shaped cross section and including, a firsthollow cylindrical portion fitted to an outer peripheral surface of theinner race, a second hollow cylindrical portion fitted to an innerperipheral surface of said outer race, an annular portion connecting thefirst hollow cylindrical portion to second hollow cylindrical portion,and axial grooves which extend through to opposite ends of the firsthollow cylindrical portion and are formed at a plurality ofcircumferential positions at least in an inner peripheral of the firsthollow cylindrical portion of each of the end bearings, each of theaxial grooves having a circular-arc-shaped cross section in which itsradial depth becomes larger toward a central portion of the axialgroove.
 7. The one-way clutch according to claim 6, wherein acircumferential groove having a predetermined axial width and a bottomsurface which includes portions of the axial grooves where the radialdepth becomes maximum is formed in the inner peripheral surface of thefirst hollow cylindrical portion of each of the end bearings.